Dyestuff compositions in the form of a dye paste, or cake, typically contain as major constituents a dispersed dye or vat dye, a dispersant, and a filler, or diluent. Fillers or diluents basically are ingredients to dilute a milled dyestuff composition to a certain color value or dye strength which is accepted as a standard and which do not interfere with the dispersion phenomena of the dyestuff in use. Such dyestuff formulations also generally contain a humectant which is employed in the liquid dye paste, or cake, to prevent the dye from drying out, such as may occur around the edges of a dye drum. Without a humectant, the dry dye material would flake back into the container resulting in insoluble particles and higher local dye concentrations which subsequently produce an uneven distribution of color bodies in cloth dyeing and a specking appearance.
In the past, dyestuff fillers have been produced from the spent liquor resulting from the sulfite pulping of wood, as disclosed in U.S. Pat. No. 3,156,520 to Blaisdell. More expensive organic materials, such as napthalene sulfonates, also have been employed as fillers in dyestuff compositions. Recently, it has been proposed to provide a dyestuff filler having humectant properties as a by-product of a kraft pulping process employed in the paper-making industry. Commonly assigned U.S. Pat. No. 4,007,004 describes a process for treating kraft black liquor to remove a substantial amount of the lignin portion and to stabilize the material against fiber staining and dye reduction to make it suitable as a filler in dyestuff compositions. In particular, the patent describes a process wherein kraft black liquor residue is acidified to a pH of about 9 to 10 to form a lignin precipitate and a filtrate, the filtrate is separated from the lignin precipitate and treated with a solubilizing agent, such as sulfur dioxide, to solubilize the remaining lignin, and the filtrate is thereafter oxidized to stabilize the filtrate. The stabilized filtrate is heated to evaporate water and obtain a final product having a solids content of about about 40% to 65%. The resultant filtrate material is then used as an aqueous solution, or the aqueous filtrate may be further concentrated by spray-drying to yield a solid filler material.
Although the filler materials produced in accordance with the process described in U.S. Pat. No. 4,007,004 function exceptionally well in dyestuff formulations to provide good humectancy with low fiber staining and low azo dye reduction, the storage shelf life of such products is limited. In particular, the liquid filler products contain substantial amounts of inorganic salts, e.g., Na.sub.2 SO.sub.3, which tend to crystalize under extended periods of storage at low temperatures, reducing the stability of the liquid filler product and its usefulness in dyestuff compositions. Salt crystalization of inorganic matter components causes settling in the humectant product with storage. The abundance of inorganic matter also causes thickening of the dye paste which results in loss of fluidity. As to the solid filler products produced in accordance with U.S. Pat. No. 4,007,004, such products quickly absorb moisture under normal conditions of humidity, and thus must be carefully stored and contained to preserve their value as a filler/humectant in the dyestuff compositions.